This invention relates to chromatography and more particularly to chromatographic columns having particular utility in preparative gas chromatography.
Previously, there have been essentially two formats of gas chromatographic columns. The more efficient format is that of an open tubular column with the walls coated with the stationary or fixed phase material. This format, sometimes referred to as a Golay or capillary column, is used for chemical analysis in which small samples are sufficient.
When the output of a capillary column is not sufficient for the desired analysis or when large outputs are required for further chemical processes as in preparative scale chromatography, the preferred format has been that of a tube packed with porous particles or granules impregnated or coated with the fixed phase material. This format, generally referred to as a packed column, has the advantage of relatively large throughput, but is slower and less efficient. Typically, with equal pressures being applied at the inlet of the columns, a separation requiring one minute with a capillary column will require several hours with a packed column.
The poor efficiency of the packed column is explainable by certain nonuniformity characteristics of this format. Firstly, there is the circumstance that any one rivulet of gas snaking its way among the packing granules alternately encounters very narrow passages between three contacting granules which offer high resistance to flow and large passages which require relatively long times for the sample molecules to diffuse to and from the fixed phase which is coated on the walls of these larger passages. In contrast, the single passage of a capillary column is of uniform dimension and this single dimension determines both the resistance to flow and the diffusion time to and from the wall. Secondly, there is the circumstance that the various rivulets of gas which may have a common origin and which meet again further along the column may have required appreciably different times for their separate travels. These travel time differences cause an unwanted spread of the various separated components in space along the column and eventually in time at the column exit and consequently the components may merge into each other instead of being clearly separated. Thus, there are some undesirable attributes of lengthwise and crosswise nonuniformity of the column.
From time to time there have been suggestions to provide a column of higher throughput and high time-wise efficiency by manifolding a number of like capillary working in parallel as a single column. However, this suggestion has not been successful. Firstly, such a column would be cost prohibitive, e.g., the cost of one hundred capillary columns would be prohibitive. Secondly, the task of trimming such a large number of columns so that they would have the same time of passage for all the components of a given sample would be practically hopeless.
Accordingly, it is an object of the present invention to provide a new and improved chromatographic column.
Another object of the invention is to provide a chromatographic column having high efficiency and relatively large throughput suitable for preparative scale chromatography.
A further object of the invention is to provide a chromatographic column having multiple uniform passageways with crosswise communication for attaining uniform frontal distribution of separated components. Included in this objective is the provision of passageways having a high degree of lengthwise and crosswise uniformity.
A still further object of the invention is to provide such a chromatographic column which is economical to manufacture and efficient in operation.
A still further object of the invention is to provide a new and improved technique for forming a chromatographic column which is economical and efficient.
Other objects will be in part obvious and will be in part pointed out more in detail hereinafter.
Accordingly, it has been found that the foregoing and related objectives and advantages can be obtained in a chromatographic column comprising a housing having an inlet and an outlet end and a plurality of uniform fluid passageways extending axially within the housing between the inlet and outlet ends. The passageways are coated with a stationary phase material and lateral openings disposed longitudinally along the passageways laterally interconnect adjacent passageways to permit fluid communication and/or molecular diffusion therebetween. In a preferred embodiment of the invention, the plurality of the fluid passageways are formed by a configuration of fiber layers disposed about an elongated central core element extending longitudinally within the housing. The fiber layer configuration comprises an innermost layer having a plurality of fibers helically wound about the central element with the fibers being in predetermined spaced disposition for forming a fluid passageway between adjacent fibers. A plurality of outwardly successive fiber layers are disposed about the innermost layer with each successive layer having a plurality of fibers helically wound in reverse hand relative to the previous adjacent layer and in predetermined space disposition for forming a fluid passageway between adjacent fibers with a plurality of lateral openings fluidly cross-connecting overlapping longitudinal fluid passageways.